How to create a Pacman-esque clock icon
Update:

The original method did not work due to a limitation of blender's interaction with the Carve library (used for boolean operations). Here is an updated technique.

Example file



You can do this using Boolean modifiers:


Add a cylinder and a cube, then move the cube 1 BU on the X and -1 on the Y. With the cube selected, enter edit node and delete one edge:


Then select one of the remaining two face and press P> Selection:


With the 3D cursor in the middle, select each cubeface/plane object and press CtrlShiftAltC to snap the object origin to the 3D cursor:


Add a Union boolean modifier to plane 1 (it doesn't matter which plane is plane 1 and which is plane 2, but once you decide you shouldn't switch) and select plane 2 as the target object:


Add a Difference boolean modifier to the cylinder and select plane 1 as the target object:



Optionally add an Edge Split modifier to get rid of the dark shadows (only visible when the mesh is smooth shaded) caused by the poor topology produced by the boolean operation.
Insert Rotation keyframes (I> Rotation) to animate the rotation of either plane:

For example:


On frame 1 with one plane selected insert a rotation keyframe (I> Rotation)
Go to a later frame and rotate 360&deg; on the Z (RZ360)
Insert another rotation keyframe (I> Rotation)